The property of having different mechanical behaviour in different directions, characteristic of FDM-printed parts and composite materials.
Anisotropy means mechanical properties (E, UTS, σ_y, toughness) vary with direction. An isotropic material has the same properties in all directions. FDM parts are orthotropic: different properties in X, Y, and Z axes. The degree of anisotropy depends on layer adhesion quality, print temperature, cooling rate, and material. Typical FDM Z/XY tensile strength ratio: 0.3–0.7 depending on material and process.
Anisotropy must be designed for: place the weakest direction (Z) so the lowest applied stress acts there. FEA of FDM parts requires orthotropic material cards, not isotropic ones. The ASTM D638 test standard requires specimens in three orientations to fully characterise FDM anisotropy. CF-reinforced filaments are highly anisotropic: fibres align in extrusion direction, giving ~10× higher E in that direction.
Using isotropic material data for FDM in FEA significantly overestimates Z-direction strength and stiffness. Print orientation decisions made late in the design process often cannot be reversed without tool redesign. Surface roughness and support scars further reduce strength below already-low bulk Z values. Anisotropy is temperature-dependent: high-temperature printing reduces the Z/XY gap by improving layer fusion.
Related terms: Young's Modulus, Tensile Strength, Isotropy, Poisson's Ratio
| Field | mechanics, engineering, 3D printing |
|---|---|
| Also called | Mechanical Anisotropy, Directional Dependence |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert